This invention relates in general to vehicle brakes and, in particular to, a method of producing a rotatable brake component and bearing assembly.
It is known to cast a rotatable brake component (e.g., a rotor or drum) with an integral hub portion. A conventional integral hub and rotor includes an axially extending hub, a radially extending mounting surface, and a radially extending outer disc which can be integrally cast as one-piece during a casting operation. The hub includes a centrally located bore formed therein, and a plurality of equally spaced lug bolt receiving holes are formed in the mounting surface circumferentially about the bore. The outer disc defines a pair of brake friction plates having opposed braking surfaces. The brake friction surfaces and the mounting surface are machined to be parallel to one another and perpendicular to the rotor axis.
When used with preassembled cartridge type of bearing units, a fully machined integral hub and rotor having preinstalled lug bolts is assembled and installed on a vehicle in the following manner. First, the cartridge bearing unit is installed in the bore of the hub of the rotor. The cartridge bearing unit can either be a pregreased sealed-for-life cartridge bearing, or of the type having a pair of bearing elements, either ball bearings or tapered roller bearings, disposed between an inner bearing race or cup and an outer bearing race or cup.
The rotor and bearing are then installed on a wheel spindle, and a nut is threaded onto the end of the spindle and tightened to pre-load the bearing assembly to predetermined specifications. Also, the nut functions to secure the rotor to the wheel spindle for rotation therewith. Next, the disc brake assembly, which includes a brake caliper slidably supported on a pair of pins, a pair of brake pads, and a hydraulically actuable piston, is secured via an anchor plate to a fixed part of a vehicle.
When fully assembled on the vehicle, the friction plates of the rotor are disposed adjacent the brake pads of the disc brake assembly and separated from engagement therewith by a predetermined normal brake running clearance when the piston is not actuated. During operation, when the piston of the disc brake assembly is hydraulically actuated, the brake shoes take up the normal running clearance and frictionally engage the friction plates.
In order to provide the normal brake running clearance, the rotor needs to be manufactured to tight specifications. In particular, the brake friction plate surfaces need to be oriented in a perpendicular relationship relative to the axis of the rotor, and in a parallel relationship relative to one another. If these tight specifications are not maintained in the friction plate surfaces, excessive lateral runout or excessive thickness variations in the friction plate surfaces of the rotor can occur which can lead to undesirable results. For example, premature or uneven wear of the brake pads can occur, or undesirable noise, vibration, or brake shudder caused by engagement of the brake pads with the friction plates when the brakes are not applied can occur.
When used with component type of bearings, it is known to assemble an integral hub and rotor by having the supplier initially finish machine the bore of the hub, and then rough machine the friction plates surfaces and the wheel mounting surface. Next, a pair of outer bearing cups are press fit into the hub bore. Then, the rotor and outer bearings cups are supported on a tool having an outer surface adapted to support the rotor relative to the outer bearing cups. Next, the brake friction plate surfaces, wheel mounting surface, and lug bolt holes are finish machined. Lug bolts are then press-fit or secured in the lug holes by retaining clips and the rotor is shipped to the assembly plant where the bearings elements and inner cups are installed. The rotor is then installed on a vehicle, and finally, the bearings are loaded to manufacturers specifications.
As a result of manufacturing an integral hub and rotor and bearing assembly in this manner, the finish machining of the friction plate surfaces, the wheel mounting surface, and the lug bolt holes are in a predetermined relationship relative to the location of the supplier installed outer bearing cups. However, after the bearing elements and the inner bearing cups are installed at the assembly plant, the location of the outer bearing races may have changed. Therefore, the runout and parallelism of the brake friction plates may be outside the desired specifications. Also, the wheel mounting surface may not be sufficiently parallel to the surfaces of the brake friction plates. In addition, there exists the possibility of the bearing elements not being properly greased, or not being properly loaded.